Polymers for Microelectronics - American Chemical Society

Chapter 16

Photochemical Control of a Morphology and Solubility Transformation in Poly(vinyl alcohol) Films

Downloaded by FUDAN UNIV on December 16, 2016 | http://pubs.acs.org Publication Date: November 23, 1993 | doi: 10.1021/bk-1994-0537.ch016

Induced by Interfacial Contact with Siloxanes and Phenol—Formaldehyde Polymeric Photoresists James R. Sheats Hewlett Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94304 Poly(vinyl alcohol) (PVA) is found to undergo a dramatic change in morphology when prepared as a thinfilm(~1000Å)between a siloxane polymer and an acid-generating novolak photoresist, and heated to 115 °C or more for a few minutes. When the siloxane is stripped off in chlorobenzene, the exposed PVA film is wrinkled and insoluble in water (although soluble in acetone). This effect is entirely prevented if the resist is exposed (before heating the films) to a lithographic dose of deep-ultraviolet (DUV) radiation; patterns can be produced in this way from optical images as small as 0.3 μm. The effect is seen with at least two siloxanes and two resists: poly(phenylsilsesquioxane) (PPSQ), poly(diphenylsiloxane) (PDPS), Shipley SAL-601, and AZ5214E. No effect is seen if either the top or bottomfilmis omitted, and no effect is seen when the topfilmis poly(methyl methacrylate) (PMMA), nor when the bottom film is AZ1350. Auger spectroscopy shows trace amounts of Si at the surface of the insoluble film, as well as some N. Atomic force microscopy (AFM) images of the morphology are presented. The transformation appears to be a consequence of the response of polymer conformation to poor solvents, delicately directed by small interfacial concentration gradients.

Resists based on the photochemical generation of acid, which then catalyzes a suitable change in polymer properties, have come into widespread use in recent years; their advantages include much greater sensitivity and considerable flexibil ity in resist design, as evidenced by the wide variety of systems that have been designed (1-3). Although there is an a priori concern that the acid might diffuse over sufficient distances to cause loss of resolution, it has been shown in at least some cases that the diffusion range is no more than a few nanometers (4). A second major development in photolithographic chemistry has been that of image enhancement by photobleaching. A number of different variations on this theme exist; the primary ones are contrast enhancement (CEL) (5), photo chemical image enhancement (PIE) (6-9), and built-on mask (BOM) (10). C E L was the first of these to appear; in this process a polymer containing a bleachable dye is spun on top of the resist, and both are exposed together. We originated the PIE system shortly thereafter; it likewise uses a top layer of 0097-6156/94/0537-0235$06.00/0 © 1994 American Chemical Society Thompson et al.; Polymers for Microelectronics ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


236

POLYMERS FOR MICROELECTRONICS

bleachable dye, but only the dye is exposed in the imaging camera, and the resist is exposed by flood exposure during which the dye image is "fixed" so that it cannot further degrade. The result is better performance at the expense of a flood exposure. In both cases, as well as with the two-layer portable conformable mask (11, 12) and other two-layer processes (1-3) there is concern about intermixing of the layers: it is not easy to devise solvent systems that are adequate for the respective polymers that also do not result in some interpentration of the two layers, with resultant scum or other deleterious effects on resist development. To circumvent this, a barrier layer of a water-soluble polymer such as P V A is often used in between. We used this approach in our early development work on PIE (7), and discovered as a consequence some unexpected effects on polymer morphology that may reveal fundamentally interesting features of interfacial layers. When P V A is placed on top of certain photoresists, and a siloxane polymer on top of that, and the system baked under conditions similar to the typical post-exposure bakes associated with the resist, the P V A undergoes (after stripping the siloxane in chlorobenzene) a dramatic change, becoming wrinkled and insoluble in water (but soluble in acetone). Most remarkably, this effect can be completely prevented if the system is irradiated before the bake, with a D U V dose suitable for exposing the resist. Since neither P V A nor the siloxane have any photoreactivity at all at those wavelengths and doses, it follows that the photochemical change in the resist is felt throughout the ~ 1000 A P V A layer thickness. In this paper we attempt to elucidate this remarkable phenomenon by systematically varying the composition of the bottom and top layers, by Auger analysis of the surface, and by A F M images of the topography. The results have a bearing on interfacial polymer chemistry and suggest the extent to which small variations in composition may dramatically affect solubility and morphology. EXPERIMENTAL DETAILS

PPSQ (M 1200-1600, with "high ladder content") and PDPS (M 1000-1400, silanol terminated) (Petrarch Chemicals) were spun from chlorobenzene solution to thicknesses of ~ 5000-8000 A. For most experiments the PPSQ was mixed with ~ 22-25 wt.% diphenylanthracene (DPA; Aldrich) for historical reasons (this is the formulation used in PIE); however the effect is observed without DPA. The source of P V A was General Electric's barrier coat for use with C E L (5) (these material are now sold by MicroSci, Inc. (13)); spun at 5000 rpm the thickness was 950 A (assuming n = 1.51) (14). AZ5214E was purchased from A Z Photoresist Products. The other acid-generating resist was obtained from Shipley; for the initial experiments it was referred to as ECX-1023 (15,16); later this became a standard commercial product SAL-601, which was used in some experiments. Despite possible changes in formulation during the intervening 4-5 years, the results were at least qualitatively the same. We will make clear which was used in each experiment; however the discussion will not distinguish between them. Resist thickness was typically ~5000 A for SAL and 1.2 /im for w

w

r

Thompson et al.; Polymers for Microelectronics ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


16.

SHEATS

Photochemical Control of Morphology Transformation

237

A Z . MF-312 (Shipley) is a typical full strength alkaline developer for novolak resists. All experiments used standard Si wafers as substrates (in one case with a ~ 1000 A thick thermal oxide). In some cases, a layer of hardbaked (~200 °C, 2 hrs, oven) Hunt HPR-204 was applied first. (A list of each set of films used is given in the Appendix, along with a summary of the results from the associated experiments.) For the experiments using ECX-1023, the resist and P V A were both softbaked at 70 °C for 30 min. in a convection oven; the PPSQ layer was not softbaked. Postbakes (i.e., the bake that produces the effect) were in all cases done on hotplates controlled to ± 1 °C. The experiments with SAL-601 and AZ5214E used a hotplate also for the softbakes. AZS214E was softbaked at 105C for 60 sec, and SAL-601 at 115C for 60 sec. D U V exposure (Lumonics excimer laser, KrF) energy was monitored by a Laser Precision pyroelectric joulemeter (RJ7200). Thickness was measured with a Nanometrics Nanospec. Actual thicknesses in the multilayer stacks are not exact since the refractive indices of the materials are not identical, while a single index is used by the Nanospec (1.64); where possible we provide corrections based on known indices. A Digital Instruments Nanoscope III was used for atomic force microscopy. RESULTS Smooth, optically homogeneous films are formed when the three layers are prepared as described, and they remain homogeneous through postbakes of up to 125 °C for several minutes. However, when the top layer (PPSQ or PDPS; most experiments were done with PPSQ but the result with PDPS was visually the same) is removed (after the bake) by rinsing briefly with chlorobenzene, the surface appears gray or a dull silver color. ("Brief rinsing" means, for example, several seconds under a squeeze bottle.) By microscope one sees the wrinkled or convoluted morphology shown in the photos in Figure 1. At the same time, this film is found to be insoluble in water, but soluble in acetone: brief rinsing washes it away instantly. (The untreated P V A does not change thickness after 30 sec. continuous rinsing in acetone, although the surface develops some crack- or ridge-line features visible in the microscope). That the film consists mostly, if not entirely, of PVA, is evidenced by two factors. First, the thickness is close to the same as the original P V A thickness (the Nanospec thickness, which averages over a 20 fim spot, for the film on E C X in Figure 1 is 1300 A). Second, Auger spectroscopy analysis shows that there is only a small amount of Si at the surface of the film. (This data is discussed in more detail below.) If the wafer is D U V irradiated with at least 10 mJ/cm (incident on the resist) before the bake, the wrinkled film does not appear: the appearance after chlorobenzene rinse is clear and homogeneous, a thickness measurement corresponds to approximately the resist + PVA, and a brief (~ 10 sec) water rinse leaves just the resist thickness. If the irradiation is from a pattern, patterns can be produced in the wrinkled film, as shown in Figure 2. These photos were obtained via the PIE process (7). The PPSQ contained DPA and a ketocoumarin sensitizer for 436 nm, and the trilayer was exposed (in air) in a Nikon 0.42 N.A. stepper with a resolution mask containing equal lines and spaces and isolated 2



238


Figure 1. Photos (lOOOx) of the wrinkled film on two different substrates: (right) E C X ; (left) A Z 5214E.

Figure 2. Photos (500x) of patterns printed in the wrinkled film (on ECX): (right) 0.4 /xm (top) and 0.3 fim (bottom) features (isolated spaces, isolated lines, and equal lines/spaces, from top to bottom in each set); (left) 0.5 fim features. Since this is a negative process, a line appears in the absence of exposure.


16.

SHEATS


lines and spaces down to 0.3 fim. It was then exposed under N to KrF laser light to give a dose of about 10 mJ/cm to the resist, postbaked at 120C for 3 min, and rinsed in chlorobenzene. It can be seen that even at 0.3 fim, distinct lines of P V A show up. At 0.4 fim, the isolated spaces are resolved, and at 0.5 fim even the equal lines and spaces give a detectable pattern. In all of these, the wrinkles often run at non-zero angles with respect to the trend of the lines as well as parallel, so the spaces in between lines are not completely empty, and the lines are not continuous; this is much better displayed in the A F M images (vide infra). The important point is that optical exposure of the resist (which is known to have resolution in this system down to 0.4 fim, and to 0.3 fim for isolated spaces) produces an effect that is transmitted into the P V A and throughout its thickness, so that distinguishable patterns are produced corresponding to this resolution. These patterns are quite stable in water (immersion for 30 min. has no observable effect), but are immediately removed by acetone. In an attempt to determine the origin of these phenomena, various layers were omitted or altered in composition. The effect was observed either with or without D P A in the PPSQ. PDPS gives a film with the same visual appearance as PPSQ (it was not further studied, e.g., with respect to D U V imaging). P M M A as a top layer has no effect (by "no effect" we mean that the films remain clear, and the P V A water soluble as usual, after a postbake of 125C for 3 or 4 min.). If there is no top layer (i.e., just P V A on top of resist), there is no effect. If P V A is put down on hardbaked HPR-204, and PPSQ spun over it, there is no effect. AZ5214E behaves qualitatively similarly to SAL-601 (Figure 1) (although it may be significant that the lateral scale of the wrinkles is larger), while AZ1350 as a bottom layer leads to no effect. Casting PPSQ on P V A and removing it without baking does not alter the P V A appearance or solubility. PPSQ as both bottom and top layers has no effect. Thus, it is established that i) both top and bottom polymer layers are needed, yet the effect that is observed is in the middle layer; ii) the top layer must be a siloxane polymer; iii) the bottom layer must be an acid-generating photoresist that has not been hardbaked; and iv) D U V radiation of a lithographic dose eliminates the effect, with resolution essentially equal to the aerial image resolution. There are some caveats to items (ii) and (Hi): only two siloxane polymers (PPSQ and PDPS, both of low molecular weight) and one hydrocarbon polymer (PMMA) have been tried for the top layer, and only four resists (SAL-601, AZ5214E, AZ1350, and hardbaked HPR-204) for the bottom. AZ5214E was tried for a top layer, but this fails because it becomes insoluble during the postbake (the same would of course happen to SAL). It would be useful to include some other polymers as bottom layers, but it seems clear that the acid is crucial. An Auger scan of the wrinkled film is shown in Figure 3. The atomic concentrations from peak-to-peak derivative measurements are 94.8% C, 2.7% 0,1.3% Si, and 1.3% N . The corresponding data for a P V A film on Si are 98.2% C, 1.5% O, and 0.3% Si; the latter figure is in the noise (no trace of a peak can actually be seen in the spectrum). Thus the remaining film has a surface layer that contains a small amount of Si; a short sputter etch (0.9 min.) eliminates this signal completely. It is interesting that the N signal remains (at about the same 2

2


239


240



a

10

200

400

600

800

Kinetic Energy, eV

b

•o a> >

10

p Ar 6

C

5 6

L

4r-

J

200

I

L.

400

600

800

Kinetic Energy, eV 2

Figure 3. a, Auger scan of wrinkled film; 3-10 /xm spot, 10 A / c m . Auger scan as in b, after 0.9 min. argon ion sputtering.



16.

SHEATS


241

intensity) after the sputter etch. (The absence of the expected amount of O is most likely due to degradation by the 10 keV electron beam, which was operating at about ~1 fiA current in a spot of ~5 fim diameter, with an acquisition time of 5 min. The results for the unprocessed P V A film on Si, which also show little O, support this explanation.) The N signal suggests that some of the bottom layer (which contains N in the melamine crosslinking agent in SAL, and in the diazonaphthoquinone in AZ) has mixed with the PVA. The possibility that the bottom layer is completely exposed to the electron beam in the low areas between the wrinkles is ruled out because immersion in developer (full strength MF312) for 2 min causes no change. Since SAL is a negative resist, the unirradiated regions would certainly have been developed if they were accessible to developer. We do not know exactly how close to the surface the Si is confined. Comparison to results obtained on the P V A film (nominally the same thickness) suggest that 0.9 min. etching removes a considerable portion of the film, so it is possible that Si penetrates a significant distance into it. Some A F M images are presented in Figures 4 and 5. Some of the features that can be observed are: i) the roughness is substantial: the peak to valley distance is as much as ~ 1000 A in some cases; ii) the height of the features varies, with some being only about 500 A high; iii) the wrinkles are smoothly sloped and not very steep; iv) the patterned "lines" have wrinkled areas of much smaller height in between (this is probably indicative of incomplete D U V exposure, since regions with clear-field exposure of substantially greater than 10 mJ/cm are optically quite smooth); v) an isolated line is in fact a pair of lines, with a deep (greater than the original P V A thickness) narrow trench in between; vi) the lines in the equal line and space patterns similarly are not individual, but come in pairs, with a substantially greater gap between pairs than between the members of a pair. This is a very regular and surprising effect: if the remaining film were due to a reaction such as crosslinking, a line would have a typical solid cross-section. 2

DISCUSSION The morphological transition described here is remarkable in itself, and an explanation of its origin is not obvious. It clearly involves phenomena at polymer interfaces, since it requires for its appearance the presence of specific polymers adjacent to the film that is actually transformed, yet the Auger data demonstrate that the interpenetration is not great (at least for the top layer). It is clearly not a chemical cross-linking process, since the film is fully soluble in acetone. Even more remarkable, however, is the photochemical effect. There seems to be no plausible candidate for this effect (at least for its initiation) other than the well-known photoresist reactions. SAL functions by photochemically generating a protonic acid that then catalyzes crosslinking reactions during postbake. AZ5214 operates by changing the resist solubility, but the basis of this change is the conversion of a naphthoquinonediazide into an indenecarboxylic acid of relatively low pK, so a protonic acid is still produced (17). AZ1350, on the other hand, produces only a much weaker acid. The strong acid somehow leads to a




242

Figure 4. (a) A F M image of the wrinkled film (taken in an area of no D U V exposure). Note the exaggerated vertical scale (50 nm/div.; horizontal 2.5 /im/div.). A cross-section shows profiles as in Fig. 4c, with heights varying from ~400 to 1000 A . (b) Part of the same image as in Fig. 4a, but with vertical scale in the same proportion as the horizontal.


SHEATS


243


16.

Figure 4c. Magnified view (and cross-section) of one of the "wrinkles" in Figure 4a. Vertical scale on the cross-section is in nm (50 nm/div.).



244


Figure 5a. A F M image and cross-section of patterned line (mask dimension 0.7 fim). The area away from the line, nominally exposed (and therefore free of wrinkled film) still has a considerable amount of it present. Because of the nature of the imaging, it is expected that this region should receive less than a full exposure (the amount received by a large open field), and so there is some film present. Note the trough in the center of the line; this feature is quite straight oyer the entire image (cf. also Fig. 5b). Its peak-to-valley height is close to 2500 A . This is a larger variation than seen anywhere in the unpatterned region shown in Figure 4. (Vertical scale of cross-section is 250 nm/div.).



16.

SHEATS


245

Figure 5b. Patterned lines and spaces (mask dimension 0.7 fim). By comparison with Figure 5a, it appears that the deep valleys, which naively would seem to be the spaces, are actually the centers of the lines, the sides of which touch each other in an irregular fashion.



246


prevention of the morphology transformation in the P V A film. A priori, one might have expected that acid could catalyze the crosslinking of PVA, leading to reduced solubility. However, exactly the opposite trend is seen. The nature of the transformation is not well understood at this stage. Certainly the phenomenon is worth understanding, in view of its unusual characteristics; a full explication may provide useful insight into polymer interfaces, diffusion, thermodynamics and kinetics. The A F M images show that smoothly rounded domains have formed, and both the solubility and Auger results are in agreement with the assumption that the wrinkled film has a composition that is no longer pure PVA. A plausible hypothesis, then, is that during the bake there is significant interpenetration of P V A and siloxane at the interface, as well as some migration of the molecular components of the resist into the PVA. ( Note that although the Auger data indicate the presence of an N-containing compound throughout the entire P V A film, it is possible that this is due to the nonhomogeneous morphology and the Auger spot size. According to the A F M images, the film has both high and low spots on the micron scale; the low spots must be fairly thin ( « 1 0 0 0 A). The Auger beam covers several microns, and therefore sees both thick and thin regions; the N signal may be entirely from the thin regions.) The diffusion coefficient required to account for penetration of about 500 A is of the order of 10" cm /sec. (for a 200 s. bake). For small molecules (such as the monomeric resist components) this is a quite reasonable number, either above or below T (cf. measurements on camphorquinone in polycarbonate (18), which are in the range of 10" - 10" above T and 10" - 10" below). T of P V A is 85C (79). The situation is less clear with polymer diffusion. PPSQ apparently does not have a distinct T (20), but remains glassy up to its thermal decomposition temperature (this report is for high M material). Wang, et al., ( ) obtained diffusion coefficients of ~ 1 0 " cm /sec for high M poly(butyl methacrylate) in latex particles, at temperatures well above T . It is possible that the low M siloxanes used here diffuse at substantially higher rates. Thus the postulated diffusion is plausible albeit not assured. The interfacial regions thus formed might then be just soluble enough in chlorobenzene for it to penetrate into the nominally P V A layer. As it does so, domains would form with P V A in the interior and a surface region that contains a small amount of siloxane and nitrogen-containing compounds from the resist. This surface would have enough non-PVA composition to be insoluble in water but soluble in acetone (and the mixture form acetone-soluble aggregates). The A F M images are consistent with this picture of a phase separation process. The simplest mechanism to account for the protection afforded by D U V exposure is to assume that the bake-induced crosslinking of the exposed resist inhibits molecular mobility so as to prevent migration into the PVA. This would then not require that acid diffuse over large distances, and also avoids the problem of what type of reaction might give these results. It would be necessary for the rate of mobility inhibition to be rapid compared to the rate at which interpenetration occurs. The trough in the center of the patterned lines can be understood in this context. The concentration of penetrant from below will be highest in the center 13

2

g

11

12

12

13

g

g

g

w

21

15

2

w

g

w



16.

SHEATS


247

of the line, and the rate of penetration of chlorobenzene will then be highest there; thus one expects that the edges of the phase separated domains should be along that line (they begin forming there). Although the details remain to be filled in, this picture of interfacial diffusion and the resulting thermodynamic instability leading to phase separation accomodates the data, and we know of no other general hypothesis that is similarly consistent. One major question is why both top and bottom films are required, yet the two together have such a dramatic effect. To account for the formation of domains that are impervious to water from all sides, we have assumed that chlorobenzene is initially able to dissolve (or at least permeate and interact with) the entire film, which implies that no pure P V A is left at the end of the bake. The data suggest that penetration from both directions is necessary to accomplish this condition. If this is the case, it would be interesting to determine why one cannot get the same effect by baking longer with a single layer: perhaps the diffusion is self-limiting. Another issue is how the relatively small amount of non-PVA material that is apparently left in the wrinkles is able to solubilize the film in acetone. X-ray photoelectron spectroscopy (XPS), which is not available to us, would be very useful in determining surface compositions in more detail and would shed a great deal of light on these aspects. SUMMARY A morphology and solubility transformation in thin films of PVA, induced by the proximity of films of polysiloxane on one side and certain photoresists on the other, coupled with heat treatment and immersion in chlorobenzene, has been described. The effect is eliminated by exposure of the resist with a typical lithographic radiation dose. Patterns (albeit irregular and distorted) are produced from an image with features of only ~0.3 /im. Although we cannot ascertain the mechanism with substantial confidence, and many perplexing questions remain, the process appears to involve diffusional intermixing of polymers (and monomers) from the adjacent layers, followed by phase separation upon contact with chlorobenzene. The photoeffect is suggested to be the result of resist crosslinking preventing the intermixing on the resist side, although migration of photoproducts into the PVA has by no means been ruled out. To provide further illumination, more detailed surface studies, especially using XPS, will be required. Photoluminescence (21) might also be useful if the system will bear the appropriate reporter molecules. ACKNOWLEDGMENT I thank John Turner and Paul Soo for obtaining the Auger data and help in interpretation, and Hua-Yu Liu for samples of SAL-601. APPENDIX We summarize here the specific film stacks and experiments. The symbols e and 0 are used to indicate no effect and a positive effect (appearance of wrinkled film), respectively. The order of films is from top to bottom.

American Chemical Society Ubrary Thompson et al.; Polymers for Microelectronics

ACS Symposium Series; American Society: Washington, DC, 1993. 1155Chemical 16th St.. H.VL


248


1) (PPSQ + D P A ) / P V A / E C X / H P R 2 0 4 / S i ; used in imaging experiments (125C, 3 min. bake; 2 min. development in MF-312). HOC, 3 min. bake: e . 120C, 3 min.; 125C, 3 min.; 120C, 8 min.: e. 112C, 4 min.: e, but film slowly (after many minutes) came off in MF312; not affected (after ~30 min.?) by warm water. 115C, 3 min.: e, but film came off slowly in MF312 and was affected by warm water (flakes came off; film did not dissolve or come off completely). Both of these films were judged "semi-opaque"; they were not examined by microscope, but may have been less wrinkled. 2) (PPSQ + D P A ) / P V A / E C X / S i ; 125C, 3min. bake: e. 3) P V A / E C X / S i ; 125C, 3min. bake: e. 4) P V A / S i ; 125C, 3 min. bake: e. MF312 removes P V A completely in ~10-15 sec. 5) PPSQ/Si; 125C, 3 min. bake: e. 6) (PPSQ + DPA)/Si; 125C, 3 min. bake: e. 7) (PPSQ + DPA)/PVA/HPR204/Si; 125C, 4 min. bake: e. 8) (PPSQ + D P A ) / P V A / S A L / S i ; 125C, 4 min. bake: e. Thickness of P V A / S A L : 6553 ± 6 A (7 meas.), using n = 1.64. SAL alone: 5703 ± 15 A (7 meas.). This implies a P V A thickness of 850A, but the correct refractive index for P V A is 1.51. (14) Thickness of P V A alone (using n = 1.51) 950 ± 17 (9 meas.); 939 ± 2 for 6 of those measurements. 850 X (1.64/1.51) = 923, in close agreement with 939 or 950. Thickness of this sample after chlorobenzene rinse (using n - 1.64) 6470 ± 86A (7 meas.). Thickness of SAL after bake is 5446 ± 18 A (7 meas.) (there is some loss of thickness due to the crosslinking reaction), so this implies 1024A for the wrinkled film thickness, or 1112A if corrected to n = 1.51 (it is not obvious that this value applies to the altered film). 9) P D P S / P V A / S A L / S i ; 125C, 4 min. bake: e. 10) P M M A / P V A / S A L / S i ; 125C, 4 min. bake: e. 11) (PPSQ + D P A ) / P V A / A Z 5 2 1 4 E / S i 0 ; 125C, 4 min. bake: ©. After the chlorobenzene rinse, the following thicknesses (in A) were measured (n = 1.64) after various times of immersion in water (9 measurements for each): 0 sec: 12909 ± 284; 30 sec: 12653 ± 268; 60 sec: 12510 ± 298; 0.5 hr. more: 12442 ± 223; 24 hrs. more: 12072 ± 223. However, the visual appearance under the microscope is the same as before water treatment, so the meaning of these changes is unclear; the Nanospec measurement of such a nonuniform film is somewhat problematic. Clearly the solubility is small at most. 12) PPSQ/PVA/AZ1350/SiO : 8. 13) P P S Q / P V A / P P S Q / S i 0 : e. There is an interesting sidelight to this experiment: there were a large number of particles in the P V A film in this case, and wrinkled, water-insoluble material was formed around the particles after the chlorobenzene rinse. This observation provides strong support for the hypothesis in the text, since one expects that chlorobenzene may easily penetrate along the edge of a particle (i.e., the particle serves the same purpose as the interfacial mixture). r

r

o

r

r

2

o

r

2

2

REFERENCES 1. Iwayanagi, T.; Ueno, T.; Nonogaki, S.; Ito, H.; Willson, C.G.; in "Electronic and Photonic Applications of Polymers", ed. M.J. Bowden and S.R. Turner, ACS Adv. Chem. Ser. 1988, 218. Thompson et al.; Polymers for Microelectronics ACS Symposium Series; American Chemical Society: Washington, DC, 1993.


16.

SHEATS


249

2. Reichmanis, E.; Thompson, L.F. Ann. Rev. Mat. Sci., 1987, 17, 235. 3. Sheats, J.R. Solid State Technology 1989, 32 (6), 79-86. 4. Umbach, C.P.; Broers, A.N.; Willson, C.G.; Koch, R.; Laibowitz, R.B. J. Vac. Sci. Technol. 1988, B6, 319-322. 5. West, P.R.; Griffing, B.F. Proc. Soc. Phot. Instr. Eng. 1983, 394, 39-44. 6. Sheats, J.R.; O'Toole, M.M.; Hargreaves, J.S. Proc. Soc. Phot. Instr. Eng. 1986, 631, 171-177. 7. Sheats, J.R. Polym. Eng. Sci. 1989, 29, 965-971. 8. Sheats, J.R. Proc. SPIE 1989, 1086, 406-415. 9. Sheats, J.R. Amer. Chem. Soc. Symp. Ser. 1989, 412, 332-348. 10. Vollenbroek, FA.; Nijssen, W.P.M.; Kroon, H.J.J.; Yilmaz, B.; Microcircuit Eng. 1985, 3, 245. 11. Lin, B.J. Proc. Soc. Phot. Instr. Eng. 1979, 174, 114. 12. Bartlett, K. Hillis, G.; Chen, M.; Trutna, R.; Watts, M.; Proc. Soc. Phot. Instr. Eng. 1983, 394, 49-56. 13. MicroSci, Inc., 10028 S. 51st St., Phoenix A Z , 85044. 14. Bohn, L. in Polymer Handbook (2 ed.), ed. J. Brandrup and E . H . Immergut (Wiley, New York, 1975), p. III-242. 15. Feely, W.E. Polym. Eng. Sci. 1986, 16, 1101. 16. Liu, H.-Y., DeGrandpre, M.P.; Feely, W.E. J. Vac. Sci. Technol. 1988, B6, 379. 17. Balch, E.W.; Weaver, S.E.; Saia, R.J. Proc. Soc. Phot. Instr. Eng. 1988, 922, 387-394. 18. Wang, C.H.; Xia, J.L. Macromolecules 1988, 21, 3519-3523. 19. Lee, W.A.; Rutherford, R.A. in Polymer Handbook (2 ed.), ed. J. Brandrup and E . H . Immergut (Wiley, New York, 1975), p. III-150. 20. Mi, Y.; Stern, S.A. J. Polym. Sci. B, Polym. Phys. 1991, 29, 389-393. 21. Wang, Y.; Zhao, C.-L; Winnik, M.A. J. Chem. Phys. 1991, 95, 2143-2153. nd

nd

RECEIVED January 21,

1993


Polymers for Microelectronics - American Chemical Society

Recommend Documents